1. Field of the Invention
The present invention relates to a punching apparatus which punches a hole at a predetermined location in a work piece by a punch constructed in a moving part (in general a ram) of a press working machine and a die constructed in a supporting part (in general a bed) of the press working machine. The present application also relates to a punching unit which is suited to the above punching apparatus.
2. Background Art
FIGS. 12 to 15 show a punching apparatus disclosed in the Japanese Patent Publication No. 2000-326296. In the punching apparatus shown in FIGS. 12 to 15, a punch unit 26 which comprises a punch 26g mounted on a punch holder (a moving part of the punching apparatus) 24 which is integrated into a non-rotatable rod 22 by bolts 23 and is fixed so as to be capable of rotating capably in rounding around the axis L along a direction of the punching operation within a predetermined angle (the angle described by the arc of the circular slot 24a in FIG. 13), also, the punching apparatus die unit 27 which comprises a die 27h is mounted on a die bed (a supporting part of the punching apparatus) 25 and is fixed so as to be capable of rotating around the axis L along the direction for the punching operation.
As shown in FIGS. 12 to 14, the punch unit 26 comprises an approximately circular base plate 26b integrated with a punch holder 24 integrated with a non-rotatable rod 22, by means of six fastening bolts 26a inserted and screwed through the slot hole 24a of the non-rotatable punch holder 24; a rectangular support plate 26d integrated with the base plate 26b by means of four fastening bolts 26c; a punch 26g having a rectangular cross-section integrated with a support plate 26d by means of two screws 26e and two washers 26f; and a work presser foot 26k, integrated so as to be movable vertically (movable upward for a predetermined length from the position shown in FIG. 12) by means of four sets of a guide pin 26i and a bushing 26j. The upper end of the each guide pin 26i is fixed to the base plate 26b, and the lower end of the each guide pin 26i slidably supports the work presser foot 26k in the vertical direction. The each bush 26j is attached to the work presser foot 26k and each bush 26j helps smooth the sliding of the guide pin 26i. Each spring unit 26h comprises a pin 26j integrated with the work presser foot 26k engages with the base plate 26b so as to be detachable in the upward direction and a compression coil Spring 26h2 disposed around the pin 26h1 and compressed between the base plate 26b and the work presser foot 26k. Here, the spring unit, the bush 26j, and the work presser foot 26k are shown only in FIG. 12.
As shown in FIGS. 12 and 15, the die unit 27 comprises a base plate 27b integrated with the die holder 25 by means of four unit presser foots 27a; a rectangular support plate 27e integrated with the base plate 27b by means of four fixing bolts and two pins 27d; a die 27h, having a rectangular hole 27h1 into which the punch 26g can be inserted to a predetermined depth, integrated with the base plate 27b by means of two screws 27f and washers 27g; a circular die cover 27j integrated with the support plate 27e by means of two fixing bolts 27i. Each units presser foot 27a comprises a block 27a1 having a claw portion at the upper part for engaging with the support plate 27e, and a pin 27a2 and a pair of fixation bolts 27a3 for fixing the block 27a1 at a home position.
As shown in FIGS. 12 and 15, the base plate 26b of the punch unit 26 and the base plate 27b of the die unit 27 are mutually connected by using four connecting pins 28 and a pair of upper and lower bushings 29 (fixed at each base plate) such that the punch 26g and the die 27h can integrally rotate by the same rotational phase (in the state where the punch 26g can accurately inter-fit the hole 27h1 of the die 27h). Each connecting pin 28 is fitted with each bush 29 so as to be able to be inserted into or drawn out from each other, so that the punch unit 26 and the die unit 27 can be independently replaced with other units.
In the above punching apparatus shown in FIGS. 12 to 15, it is necessary to connect and relatively position the punch 26h to the die 27h by operating the four connecting pins 28 and eight bushings 29. Furthermore, the bushing 29, the base plate 26b, the guide pin 26i and supporting plate 26d must be arranged between the punch 26g and each connecting pin 28, and the bushing 29, the base plate 27b, the pin 27d and the supporting plate 27e must be arranged between the die 27h and each connecting pin 28.
Because it is necessary to operate so many parts (the four connecting pins 28 and the eight bushings 29) in order to relatively position the punch 26g and the die 27h, the costs and man-hours required to constructing the punch 26g and the die 27h are increased. Because there are such many parts (the support plate 26d, the guide pin 26i, the base plate 26b, the bushing 29 for punch 26g, the connecting pins 28, the bushing 29 for the die 27, the base plate 27b, the pin 27d, the supporting plate 27e and etc) between the punch 26g and the die 27h, the dimensional errors of each parts accumulate. Because the bushing 29 located on the upper end of the connecting pin 28 supports the punch 26g and the bushing 29 located on the lower end of the connecting pin 28 supports the die 27h, the space between the punch 26g and the die 27h becomes to be too much to exactly position the punch 26g relative to the die 27h. 